What named point in the Mariana Trench is the deepest known point in Earth's seabed?

The named point in the Mariana Trench that is the deepest known point in Earth's seabed is Challenger Deep.

Challenger Deep lies at the southern end of the Mariana Trench in the western Pacific Ocean, within the territorial waters of the Federated States of Micronesia. Modern surveys place its deepest seafloor roughly 10.9 kilometres below sea level, although exact figures vary with instruments, sound-speed corrections, and location.

The feature was first sounded during the 1872–1876 voyage of HMS Challenger. A later expedition by HMS Challenger II identified the deepest basin more clearly, giving the feature its enduring name. In January 1960, Jacques Piccard and Don Walsh became the first people to reach it in the bathyscaphe Trieste.

Challenger Deep is not the name of the entire Mariana Trench; it is a particularly deep depression within it. The depression contains western, central, and eastern basins, and researchers continue refining which surveyed spot is deepest.